An LCD has the advantages of portability, low power consumption, and low radiation, and has been widely used in various portable information products such as notebooks, personal digital assistants (PDAs), video cameras and the like. Furthermore, the LCD is considered by many to have the potential to completely replace CRT (cathode ray tube) monitors and televisions.
A typical LCD includes an LCD panel, a timing controller, a gate driver, and a data driver. The LCD panel includes a plurality of thin film transistors (TFTs), and a plurality of pixels, each of which is driven by a TFT. The gate driver drives the TFT by two different voltages, namely VGH and VGL. The data driver provides a plurality of gray-scale voltages to the pixels via the activated TFTs.
In order to avoid the gate driver being latched up by the two different voltages VGH and VGL, a delay circuit is needed to delay the voltages VGH and VGL for different predetermined time periods.
As shown in FIG. 2, a typical driving circuit 200 of an LCD includes two first delay circuits 210 and a second delay circuit 220. Each first delay circuit 210 includes a first transistor 212, a first capacitor C1, a first resistor R1, and a second resistor R2. The second delay circuit 220 includes a second transistor 222, a second capacitor C2, a third resistor R3, and a fourth resistor R4.
In each of the first delay circuits 210, the first transistor 212 is a PNP (positive-negative-positive) type transistor. A base electrode “b” of the first transistor 210 is connected to ground via the second resistor R2. The first capacitor C1 and the first resistor R1 are connected in parallel, between an emitter electrode “e” and the base electrode “b” of the first transistor 212. The emitter electrode “e” of the first transistor 212 receives a first voltage signal from a first input terminal 211. A collector electrode “c” of the first transistor 212 provides the first voltage signal to a first output terminal 213. The first voltage signal can be a voltage VGH, or a voltage VDD. One of the first delay circuits 210 is used to delay the voltage VGH a first predetermined time period T1, and then send the voltage VGH to a gate driver of the LCD. The other first delay circuit 210 is used to delay the voltage VDD a second predetermined time period T2, and then send the voltage VDD to a data driver of the LCD.
The second transistor 222 is an n-channel metal oxide semiconductor field effect transistor (N-MOSFET). A gate electrode “G” of the second transistor 220 is connected to ground via the fourth resistor R4. The second capacitor C2 and the third resistor R3 are connected in parallel, between a source electrode “S” and the gate electrode “G” of the second transistor 222. The source electrode “S” of the second transistor 222 receives a second voltage signal from a second input terminal 221. A drain electrode “D” of the second transistor 222 provides the second voltage signal to a second output terminal 223. The second voltage signal can be a voltage VGL. The second delay circuit 220 is used to delay the voltage VGL a third predetermined time period T3, and then send the voltage VGL to the gate driver of the LCD.
The first and second delay circuits 210, 220 are analog circuits. The parameters of the elements of the first and second delay circuits 210, 220, such as the first and third resistors R1, R3 and the first and second capacitors C1, C2, vary in different environmental temperatures. Therefore the delay time periods T1, T2 and T3 vary with differing environmental temperatures. Thus, the delay time periods T1, T2, T3 cannot be accurately controlled.
What is needed, therefore, is a driving circuit of an LCD that can overcome the above-described deficiencies.